In recent years, from the viewpoint of environmental load reduction, there has been a need for environmentally friendly and clean liquid fuels with a low sulfur content and aromatic hydrocarbon content. From such a viewpoint, as technology which is able to produce a fuel base stock, specifically kerosene or gas oil base stock, not including a sulfur content or aromatic hydrocarbons, that is rich in aliphatic hydrocarbons, methods utilizing the Fischer-Tropsch synthesis reaction (hereunder referred to as “FT synthesis reaction”), in which carbon monoxide gas (CO) and hydrogen gas (H2) are feedstock gases, are being investigated (refer to Patent Document 1 for example).
Conventionally, as a method for producing hydrocarbon oils by the FT synthesis method, a method has been disclosed using a bubble column slurry bed reactor, in which the FT synthesis reaction is performed by blowing a synthesis gas (a mixed gas with CO and H2 as principal components) into a slurry in which FT synthesis reaction catalyst particles are suspended within the hydrocarbon oil as a liquid medium (refer to Patent Document 2 for example).
In such a bubble column slurry bed reactor, in a case where the FT synthesis reaction activity of the catalyst (FT synthesis reaction catalyst particles) during operation has decreased, it is necessary to perform temperature compensation of this activity decrease by raising the reaction temperature for example. However, if the reaction temperature is increased, there is a problem in that the chain growth probability α and the selectivity toward hydrocarbon oils with 5 carbon atoms or more (hereunder also referred to as C5+) decreases (refer to Non-Patent Document 1). An FT synthesis reaction having a high synthesis gas conversion rate (carbon monoxide conversion rate) and being able to obtain C5+ in good yields (high C5+ selectivity) is desirable from the viewpoint of economic efficiency since the product oil yield increases. Therefore, to continue to make the reaction temperature high in order to maintain the FT synthesis reaction activity of the catalyst results in the C5+ selectivity decreasing and the product oil yield decreasing, and it is not preferable from the viewpoint of economic efficiency.
Therefore, in a case where the FT synthesis reaction activity of the catalyst during operation has decreased, instead of making the reaction temperature high, it is necessary to fill the reactor with fresh catalyst. As a method of filling the reactor with fresh catalyst in this manner, conventionally, a catalyst filling apparatus and a catalyst filling method by the device disclosed in Patent Document 2 is known for example. The technology of Patent Document 2 is such that the slurry is prepared by suspending only a fresh catalyst within the hydrocarbon oil in the slurry preparation tank provided separately to the reactor, and next, by introducing an inert gas, such as nitrogen, to the slurry preparation tank, and making the pressure inside the slurry preparation tank higher than the pressure of the reactor, pressure transfer of the slurry in the slurry preparation tank to the reactor is performed.